Distronic Cruise Control Routinely Stops Working
 

I picked up a 2011 SL63AMG a couple of months ago and discovered on the long drive home that the adaptive cruise control always disengages without warning after 10 - 20 minutes of normal operation. The same thing happens any time I try to use cruise control for that length of time.

Our local dealer checked it out and showed me the analyzer result that everything was operating within prescribed limits. Of course, whenever the ignition is turned off and restarted the cruise system must reboot and it works fine again.... briefly. The message on the display simply says "Distronic unavailable - see owner's manual." I live in South Carolina, so no snow or slush buildup to interfere with the sensor. I haven't even driven in the rain yet. I suspect the sending unit is bad, but at ~ $2000 a pop, I'm hesitant to just order a replacement. Just wondering if anyone else has ever experienced this and has any suggestions?

For the moment, I'm planning to try a second Mercedes Dealership when I visit my son in Charlotte in a couple of weeks (any suggestions on Charlotte dealers?). Frankly, I'd be happy if I could deactivate the "adaptive" mode and just use a basic speed cruise setting, but it appears there's no way to do that.

Did they not take for test drive to see it not work after they found no faults?

Have them hook up their scanner and take them for a drive...

Since it takes 10-20 minutes on cruise for it to fail, i doubt the dealer is going to send a tech out with SDS connected to monitor it for that length of time. In fact, they are supposed to send out two techs when monitoring with SDS - one to drive, the other to operate the computer. I am surprised that there are no stored codes in the DTR module, though. And that is not the way it should work - it should nto shut off after any length of time.

Just out of curiosity, is anything else "blipping" when DTR shuts off? If so, it could be a different problem (like a bad EIS).

The tech indicated they did take it for a test drive, but could not get it to fail which surprised me. I'm guessing the test drive was just too brief. No other indications, e.g. "blipping" when it quits. On my single long drive after purchase, the DTR would eventually recover allowing me to activate the DTR, but then it would shut off again a short while later. The technician seemed pretty sharp, but I did not think to ask if they checked stored codes, which is why I'm thinking it's maybe worth another trip to a different Mercedes dealer, particularly if they are able to do a test drive with SDS connected. I wasn't aware that any dealer would be willing to do that.

They will (and should) use live data as a diagnostic tool. The problem is, you'll pay for that. If you are going to DIY on this car, you need to get your own scan tool. Of course SDS is the best option, but for less money (and less of a learning curve) you can get something like the iCarsoft MBII or the Autel MD802 Elite.

:ditto: Absolutely agree. At this point it would be worth it to you to get your own scan tool....will pay for itself!

Well, that's interesting. One of the first things I did when I brought the SL63 home was plug in my OBD reader - lots of data with no error codes. Just tried it again and now it's showing ....

https://cimg8.ibsrv.net/gimg/www.mbw...009a7143a5.jpg
According to Repair Pal,

https://cimg4.ibsrv.net/gimg/www.mbw...0a303d65c3.jpg
I can see where that might affect the adaptive cruise, although it seems curious this wouldn't have been picked up by the Mercedes dealer. Got a few weeks before I go to Charlotte, so I guess I'll keep an eye on this. Don't think this is something I can solve on my own, but it can't hurt to do some more research.

Thanks for the suggestion to have another look with the OBD reader.... I really like the SL, but in spite of careful research it's a little unsettling thinking there may be some problems lurking in the drivetrain.

@Bruce: That's a generic OBDII scanner that just read from the ECU (engine control unit). You need to get a scan tool that reads MBZ's proprietary systems like those that I mentioned.

Rodney - Thanks!, I see your point. Looks like iCarsoft MBII and the Autel MD802 Elite could be had for about the same price if you shop around. Intuitively, it seems the Autel would be the better choice since it appears to fit a wider range of vehicles, but I'm not familiar with either. Do you have a preference?

Update: Of course, I should have checked before asking this question - sorry. This thread provided some useful comparison feedback on the iCarsoft vs. the Autel MD802 > https://www.benzworld.org/forums/w16...arsoft-mb.html

I've not used either one, but as you found, the very resourceful guys on that W163 forum really like the Autel.

Update for posterity: - purchased the Autel scanner and picked numerous trouble codes :( , but nothing that I could readily see as being related to the Distronic. Recorded and cleared the codes with no improvement to the Distronic performance. Tried live data acquisition, but no joy there as well.

Decided to bite the proverbial bullet and take the car to another Mercedes dealer in Charlotte (Hendrick Motors) while visiting my son. They performed a "short test," and did not find any faults for the Distronic, but found a current fault in the RF SAM. Cleared the codes and were "unable to perform a second short test due to faulty RF Sam. They did perform a 20 minute test drive, without experiencing any issues with the cruise control. The service rep indicated RF Sams are more likely to fail than the Distronic sending unit. Interestingly, the Distronic worked flawlessly for 2/3rds of my subsequent 4 hour drive back home from Charlotte and then reverted to it's previous mode of cutting out every 5 - 10 minutes.

I'm inclined at this point to believe that when the dealer cleared the fault code for the RF SAM, it was able to function correctly for awhile before slipped back into the usual failure mode. It seems enough of an indication to go ahead and replace the RF SAM (quoted at $820). Did a little research to see if this was a part that our Indie Mech and I could handle on our own, but it appears from what I've read on some of the forums, the SAM needs to be programmed by a Mercedes dealer to function correctly.

Last but not least, I re-examined the original Autel data and did see the following SAM faults, but didn't have a clue what a SAM was (still not 100% clear) and since I was able to clear the fault which initially didn't reappear, those codes didn't strike me as significant.

Fault Codes(254)
B1000 Stored&Current
Control unit N10/11 (Passenger-side SAM control module) is defective.
B1013-001 Stored
Terminal 15 :Short circuit to positive

Current thinking is to schedule the RF SAM replacement in the next couple of months, hoping this solves the Distronic issue. Feel free to comment of course if anyone thinks I'm way off base - still got a lot to learn with the SL63. I'll continue to update progress or lack thereof as I work my way through this.

Hi, xxx
Its possible that the SAM creates problems on the interior CAN bus, the DTR is pretty sensitive in any communication glitches with the SBC, ESP or EGS/VGS, but this is on the engine CAN bus. However these two busses commicate via the ZGW (sorry for german abbr.) so i recomend to replace the SAM first, its also the chapest part in the chain.

Cheers, Frank
(Mine died a while ago as well, therefore i recommend also to buy a new revised part)

I think ZGW = EIS (electronic ignition switch) as that is the "gateway" between the CAN buses. For some reason, the EIS in these cars does seem to be a bit sensitive and when it fails, it causes some strange issues.

not quite, ZGW=Central GateWay is a seperate module, but before it was introduced (around 2000), the gateway was in the EZL/EIS.

Cheers, Frank

Thanks for the correction! But that does spur a question for the OP: Are you having any other unusual symptoms or malfunctions besides the intermittent dropout of Distronic?

I've not discovered any other electronic glitches so far. The original fault list from my first scan with the Autel was disturbingly long, however I expect over time some of this is normal. Just ran another scan and the only trouble code that came back after the dealer & I cleared our respective scan results was the same B1000 defective SAM module. So I'm thinking between what the dealer reported and from Frank's input, the SAM module needs to be replaced.

That's not to say there aren't some other minor issues both Mercedes dealers highlighted that are now on my list (slow hydraulic steering rack leak, leaking motor mount, worn transmission mount - probably all normal for a 7 - 8 year old car with ~ 40,000 miles). Probably the one mystery that haunts me the most after purchasing the SL is that I discovered the underside back corners of the hood looks "unpainted." Just a small area in each corner, but I don't see how it would have left the factory this way, which has me wondering if the car was in an accident previously. It had a clean Carfax and I suspect even paying out of pocket to hide any accident that would have required a new hood would have been almost prohibitively expensive. Adding to my unease, the local dealer also really struggled to perform a wheel alignment and could not get it completely in spec, but the dealer in Charlotte told me the SL's are very difficult to align and saw no evidence of a previous accident, so maybe I'm being too paranoid.

Anyhow - really appreciate the feedback. I'll update this post after I replace the SAM in a few months.

How are you resetting distronic?